Effect of the microstructure of n-butyl acrylate/N-isopropylacrylamide copolymers on their thermo-responsiveness, self-organization and gel properties in water (original) (raw)
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European Polymer Journal, 2014
We report on the synthesis of poly(N-isopropyl acrylamide)-block-poly(n-butyl acrylate) (PNIPAm-b-PnBA) amphiphilic block copolymers and their temperature-responsive selfassembly behavior in aqueous solution. Well-defined PNIPAm-b-PnBA copolymers have been synthesized by a two-step RAFT polymerization scheme. The self-assembly behavior was studied by means of static and dynamic light scattering, 1 H NMR and fluorescence spectroscopy and transmission electron microscopy. The results show that already below the lower critical solution temperature (LCST) of PNIPAm, association of the PNIPAm blocks with hydrophobic dodecyl end groups of the charge transfer agent leads to the formation of loose aggregates of PNIPAm-b-PnBA micelles, the size and density of which increase with the increasing length of the PNIPAm block. The collapse of the PNIPAm blocks above the LCST leads to the decrease of the aggregates' size and the increase of their density, but the collapsed PNIPAm chains do not allow for interpenetration of the micellar shells and no further aggregation occurs.
Applied Rheology, 2009
Thecombined effectof charged addition and molecular weight, M ... on thethermal gelatioo and gel dis50lut:lCP' cf poly(N-isopropylacrylamide) chains W3S explored by using Rheological techniques, The s)'nthesized cha rgec. derivative is pol)'(N-isoprop)'lacrylamide co-Acrylic acidI, The rheological behavior of the two macromolecuie is dea rl)' differenl: the thermal gelation of the high M .. and charged macromolecule is much more accentua· ed. This suggests that the gelation at high temperatures onl)' occurs when the inter pol)'mer aggregat e dislana is sufficiently short to allow polymer bridging: this situation can be achieved b)' different approaches, such_ increasing polymer concen t ration and increasing pol)'mer persistence length and polymer M ....
Homopolymer and ABC Triblock Copolymer Mixtures for Thermoresponsive Gel Formulations
Gels, 2021
Our group has recently invented a novel series of thermoresponsive ABC triblock terpolymers based on oligo(ethylene glycol) methyl ether methacrylate with average Mn 300 g mol−1 (OEGMA300, A unit), n-butyl methacrylate (BuMA, B unit) and di(ethylene glycol) methyl ether methacrylate (DEGMA, C unit) with excellent thermogelling properties. In this study, we investigate how the addition of OEGMA300x homopolymers of varying molar mass (MM) affects the gelation characteristics of the best performing ABC triblock terpolymer. Interestingly, the gelation is not disrupted by the addition of the homopolymers, with the gelation temperature (Tgel) remaining stable at around 30 °C, depending on the MM and content in OEGMA300x homopolymer. Moreover, stronger gels are formed when higher MM OEGMA300x homopolymers are added, presumably due to the homopolymer chains acting as bridges between the micelles formed by the triblock terpolymer, thus, favouring gelation. In summary, novel formulations base...
ATR–FTIR studies of a thermo-responsive ABA triblock copolymer gelator in aqueous solution
Polymer, 2006
A variable temperature ATReFTIR study of the gelation behaviour of a thermo-responsive ABA triblock copolymer (A ¼ poly(N-isopropylacrylamide) and B ¼ poly[2-(methacryloyloxy)ethyl phosphorylcholine]) is reported. Close inspection of selected copolymer and water bands in the temperature resolved spectra provides evidence for the dehydration of the poly(N-isopropylacrylamide) chains above a critical gelation temperature of approximately 37 C, while the central poly[2-(methacryoyloxy)ethyl phosphorylcholine]) chains remain hydrated. A blue shift in the amide I peak and a red shift in the amide II band indicate a reduction in the hydrogen bonding between the PNIPAM amide functional group and the solvent water. This is corroborated by a decrease in the intensity of the amide I peak above the gel point. Evidence of hydrophobic interactions and an indication of the source of the gelation mechanism were observed in the form of a red shift in the antisymmetric CH vibration with increasing temperature. These findings are consistent with the formation of a micellar gel network by the copolymer chains.
Polymers, 2017
In this study, seven thermoresponsive methacrylate terpolymers with the same molar mass (MM) and composition but various architectures were successfully synthesized using group transfer polymerization (GTP). These terpolymers were based on tri(ethylene glycol) methyl ether methacrylate (TEGMA, A unit), n-butyl methacrylate (BuMA, B unit), and 2-(dimethylamino)ethyl methacrylate (DMAEMA, C unit). Along with the more common ABC, ACB, BAC, and statistical architectures, three diblock terpolymers were also synthesized and investigated for the first time, namely (AB)C, A(BC), and B(AC); where the units in the brackets are randomly copolymerized. Two BC diblock copolymers were also synthesized for comparison. Their hydrodynamic diameters and their effective pK a s were determined by dynamic light scattering (DLS) and hydrogen ion titrations, respectively. The self-assembly behavior of the copolymers was also visualized by transmission electron microscopy (TEM). Both dilute and concentrated aqueous copolymer solutions were extensively studied by visual tests and their cloud points (CP) and gel points were determined. It is proven that the aqueous solution properties of the copolymers, with specific interest in their thermoresponsive properties, are influenced by the architecture, with the ABC and A(BC) ones to show clear sol-gel transition.
2009
In this work thermoassociative gel formation of a new family of aqueous temperature-responsive copolymer solutions has been investigated. This was achieved using a cationic poly(N-isopropyl acrylamide) (PNIPAm) graft copolymer recently prepared [Liu R, De Leonardis P, Cellesi F, Tirelli N, Saunders BR. Langmuir 2008;24:7099]. The PDMA þ x-g-(PNIPAm n) y copolymers have x and y values that originate from the macroinitiator; the value for n corresponds to the PNIPAm arm length. DMA þ is quarternarized N,N-dimethylaminoethyl methacrylate. The copolymer solutions exhibited cloud point temperatures (T clpt) of about 33 C, which were not significantly affected by x/y ratio or the value for n. Thermoassociative gel formation occurred above T clpt at copolymer concentrations (C copol) greater than or equal to 4 wt.%. This is a reasonably low C copol value and is a consequence of the graft copolymer architecture employed. We investigated the effect of temperature, C copol and copolymer structure on gelation and gel elasticity using variable-temperature dynamic rheology. For PDMA þ 30-g-(PNIPAm 210) 14 solutions at 39 C it was found that G 0 (elastic modulus) scales with C copol according to G 0 w C copol 3.85. The data suggested that a significant proportion of PNIPAm units is not directly involved in network formation. Thermoassociative gel formation and the gel properties for these systems appear to be governed by a balance between electrostatic repulsion involving the DMA þ units (favouring spatial extension of the copolymer backbones) and attractive hydrophobic interactions between PNIPAm side chains (favouring associative crosslink formation).
Polymer, 2004
Series of amphiphilic diblock copolymers with poly(N-isopropylacrylamide) as a hydrophilic block and a hydrophobic block consisting of either polystyrene or poly(tert-butyl methacrylate) were synthesised using RAFT polymerisations. Differential scanning calorimetry showed the chemically different blocks being phase separated in dry polymers. Light scattering and microcalorimetry studies were performed on aqueous solutions to investigate the phase behavior of the diblock copolymers. By carefully transferring the polymers from an organic solvent to water, either micellar particles or large aggregates were obtained depending on the relative lengths of the blocks. Large aggregates collapsed upon heating, whereas collapse occurred slowly within a broad temperature range in the case of micelle like structures. However, microcalorimetrically the collapse of the PNIPAM chains was observed to take place in all samples, suggesting that the shells of the micellar particles are crowded in a way which hinders the compression of the poly(N-isopropylacrylamide) chains.
Colloid and Polymer Science, 2013
Novel triblock copolymers with PEG middle blocks of 1-10 kDa and poly(N-isopropylacrylamide-co-tbutylacrylamide) statistical copolymer side arms with DP n ≈88 and different compositions, were synthesized by SET-LRP. The thermogelation properties of their aqueous solutions depended on both hydrophobic monomer content of the side blocks and molecular weight (MW) of the poly(ethylene glycol) (PEG) middle block, as proven by dynamic rheometry, DSC, and tube inversion method measurements. At constant PEG chain length, increasing TBAM proportions led to a gelation process occurring at progressively lower temperatures, as well as to a lower stability of the forming hydrogels in the case of shorter-PEG-chain block copolymers. By employing longer PEG blocks (M PEG ≥6,000 Da), stable hydrogels with the gelation temperature below 37 °C could be obtained. For a constant composition of the copolyacrylamide blocks, the dependence of the phase transition temperature (T ph ) on M PEG displayed a different shape at different polymer solution concentrations, because of the stronger variation of T ph with polymer concentration as M PEG increased. Also, the viscoelastic properties of the hydrogels resulting from 20 wt.% polymer aqueous solutions at 37 °C were stronger affected by the MW of the PEG middle block than by the hydrophobic character of the thermosensitive side blocks.
Thermoresponsive Tetrablock Terpolymers: Effect of Architecture and Composition on Gelling Behavior
Macromolecules
Thermoresponsive gels are an exciting class of materials with many bioapplications, like tissue engineering and drug delivery, but they are also used in formulation industry and 3-D printing. For these applications to be feasible, the gelation temperature must be tailored. Here, it is reported how the gelation temperature is affected and can be tailored by varying the architecture of tetrablock terpolymers. Specifically, 15 copolymers based on penta(ethylene glycol) methyl ether methacrylate (PEGMA, A block), n-butyl methacrylate (BuMA, B block), and the thermoresponsive 2-(dimethylamino)ethyl methacrylate (DMAEMA, C block) were synthesized using group transfer polymerization. Nine tetrablock copolymers of varying architectures, and one triblock copolymer for comparison, with constant molar mass and composition were fabricated. Specifically, the polymers that were investigated are (i) three polymers that contain two A blocks (ABCA, ABAC, and ACAB), (ii) three polymers that contain two B blocks (BACB, BABC, and ABCB), (iii) three polymers that contain two C blocks (CABC, CACB, and ACBC), and (iv) one ABC triblock terpolymer that was synthesized as the control polymer. Then, the five more promising architectures were chosen, and five more polymers with a slightly different composition were synthesized and characterized. Interestingly, it was demonstrated that the block position (architecture) has a significant effect on self-assembly (micelle formation), cloud point, and the rheological and gelling properties of the polymers with two of the tetrablocks showing promise as injectable gels. Specifically, the ACBC terpolymer with 20−30−50 w/w % PEGMA−BuMA−DMAEMA formed gels at at lower concentration but at higher temperatures than the ABC triblock copolymer that was synthesized as a control. On the other hand, the BABC terpolymer with 30−35−45 w/w % PEGMA−BuMA−DMAEMA formed gels at the same concentrations as the ABC triblock control polymer but at lower and more desirable temperatures, slightly below body temperature.
Reactive & Functional Polymers, 2010
Low polydispersity PNIPAM-PEG-PNIPAM triblock copolymers with PEG blocks of 1-6 kDa and PNIPAM chains of 5-30 kDa were synthesized and their thermogelation behavior in aqueous solution as a function of their composition and block length was investigated for the first time. DSC, dynamic rheometry and the tube inverting method were employed to characterize the gelation process at various polymer concentrations, and their results were compared. The thermogelation process depended mainly on the length of both PNIPAM and PEG blocks. Both association and aggregation temperatures of the PNIPAM chains decreased with the MW of PNIPAM and increased with the length of the PEG block. The amplitude of these effects depended on the molecular weights of the blocks forming the copolymer as a consequence of the partial mixing of PNIPAM and PEG chains during the association/aggregation process, while the overall hydrophilicity of the entire copolymer played only a minor role. The length of the PEG block proved also to be the most important factor for the preparation of a stable gel in 20 wt.% solutions, while the hydrophilic groups/hydrophobic groups ratio had no importance.